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Structural basis for the cAMP-dependent gating in the human HCN4 channel

Xinping Xu1, Zhanna V Vysotskaya, Qinglian Liu

  • 1Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, Virginia 23298, USA.

The Journal of Biological Chemistry
|September 11, 2010
PubMed

Insights

Researchers structurally and functionally characterized human HCN4 channels, revealing distinct cAMP-dependent gating compared to HCN2. This study provides insights into cardiac channel function and regulation.

Area of Science:

  • Biophysics
  • Molecular Biology
  • Cardiovascular Physiology

Background:

  • Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are crucial in the cardiovascular and central nervous systems.
  • HCN4 is the predominant isoform in the human heart, and its cyclic adenosine monophosphate (cAMP)-dependent gating is key to cardiac function.
  • Previous structural data on HCN channels focused on mouse HCN2 (mHCN2), leaving other mammalian isoforms understudied.

Purpose of the Study:

  • To elucidate the structural and functional characteristics of the human HCN4 (hHCN4) channel's C-terminal region.
  • To compare the cAMP-dependent gating mechanisms of hHCN4 with mHCN2.
  • To identify structural determinants responsible for functional differences between HCN isoforms.

Main Methods:

  • X-ray crystallography to determine the 2.4 Å structure of the hHCN4 C-terminal fragment.
  • Biochemical assays to assess protein interactions and function.
  • Electrophysiological recordings to analyze channel gating properties.

Main Results:

  • The crystal structure of the hHCN4 C-terminal fragment showed high similarity to mHCN2.
  • Functional analysis revealed hHCN4 exhibits a significantly reduced response to cAMP (approximately 3-fold lower) compared to mHCN2.
  • Specific residues in the loop between β4 and β5 strands were identified as contributing to these isoform-specific cAMP responses.
  • cAMP binding to hHCN4 induced a prolonged effect on channel deactivation.

Conclusions:

  • The hHCN4 channel possesses unique cAMP-dependent gating properties distinct from mHCN2, despite structural similarities.
  • The identified structural differences offer mechanistic insights into isoform-specific cAMP modulation.
  • The prolonged deactivation effect of hHCN4 upon cAMP binding may have significant physiological implications for cardiac rhythm regulation.

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